Bicycle helmet with vent

ABSTRACT

A bicycle helmet can include at least one ventilation opening and an exhaust port such that airflow enters the helmet through the ventilation opening and exits through the exhaust port, providing ventilation for a user. The orientation and location of the ventilation openings can reduce the aerodynamic drag of the helmet by delaying flow separation from the surface of the helmet and prevent airflow stagnation around the user&#39;s shoulders and neck.

FIELD OF THE INVENTION

The present invention relates to protective helmets and bicycle helmets in particular.

DESCRIPTION OF THE RELATED ART

Protective helmets of many varieties exist to provide head protection for bicyclists. However, not only must a helmet provide adequate protection from serious head injury, preferably, the helmet is light weight, comfortable, and ventilated to help the rider stay cool.

SUMMARY OF THE INVENTION

One aspect of at least one embodiment of the invention is the recognition that there exists a continuing need to develop protective bicycle helmets that increase rider ventilation without increasing the aerodynamic drag associated with conventional vent placements on bicycle helmets. In one embodiment, an aerodynamic bicycle helmet can include one or more ventilation openings or vents located on the sides of the helmet which act as an airflow control system to direct airflow into the interior of the helmet, providing ventilation for the rider. The airflow may then be exhausted from the helmet via an exhaust port located at the rear of the helmet.

Another aspect of at least one embodiment of the invention is the recognition that the ventilation openings may be oriented perpendicular to the local flow direction in order to minimize the flow disruption.

Yet another inventive aspect of at least one embodiment of the present invention is the recognition that the vents may have a small width and depth in comparison to their height perpendicular to the local flow direction in order to reduce aerodynamic drag associated with the vents.

Yet another inventive aspect of at least one embodiment of the present invention is the recognition that the airflow flowing into the helmet through the vents may exit the helmet through an exhaust port located in the wake region of the helmet.

In some embodiments, including the illustrated embodiment, a bicycle helmet is disclosed. The bicycle helmet desirably comprises a main unit having a cavity configured to receive a user's head, the main unit comprising a shell and a body, the main unit defining a front surface and a rear surface which have a parabolic profile when viewed from above when the user is in an aerodynamic position with the user's head lowered; a ventilation mechanism comprising at least one ventilation opening formed in a side surface of said main unit rear of a widest vertical cross section of the main unit, said ventilation opening having a height, a width, and a depth, and an exhaust port in a rear portion of the main unit wherein the height of the ventilation opening transverse to a local flow direction at said ventilation opening is the largest dimension of the ventilation opening; wherein said ventilation mechanism provides an airflow through said main unit due to airflow entering the main unit through the at least one ventilation opening and exiting the main unit through the exhaust port.

In other embodiments, including the illustrated embodiment, a bicycle helmet is disclosed. The bicycle helmet desirably comprises a body having a cavity configured to receive a user's head; a ventilation mechanism comprising at least one ventilation opening formed in a side surface of said main unit rear of the widest cross section of the main unit and an exhaust port formed substantially in a rear portion of the main unit, wherein said ventilation mechanism provides a flow of air through said main unit due to airflow entering the main unit through the at least one ventilation opening and exiting the main unit through the exhaust port.

In some embodiments, including the illustrated embodiment, a method for reducing aerodynamic drag while operating a bicycle is disclosed. The method is desirably achieved through providing an aerodynamic bicycle helmet comprising a body having a cavity configured to receive a user's head, a ventilation mechanism comprising at least one ventilation opening formed in a side surface of said helmet rear of the widest cross section of the main unit and an exhaust port formed in a rear portion of the main unit; placing said helmet on the user's head; orienting the user's head while operating a bicycle such that a local airflow direction at the ventilation opening is perpendicular to said opening; and allowing said airflow to enter the helmet through said ventilation opening and exit the helmet through said exhaust port.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages are described in greater detail below with reference to the drawings which are intended to illustrate, but not to limit, the present invention.

FIG. 1 is a left side elevation view of a bicycle helmet having certain features, aspects and advantages of the present invention.

FIG. 1A is an enlarged view of a central portion of the front of the bicycle helmet shown in FIG. 1.

FIG. 2 is a right side elevation view of the bicycle helmet of FIG. 1.

FIG. 3 is a lower rear left side perspective view of the bicycle helmet of FIG. 1.

FIG. 4 is a lower front right side perspective view of the bicycle helmet of FIG. 1.

FIG. 5 is a top plan view of the bicycle helmet of FIG. 1.

FIG. 6 is a front elevation view of the bicycle helmet of FIG. 1.

FIG. 6A is an enlarged view of the left side of the bicycle helmet of FIG. 1 as viewed from the front of the helmet.

FIG. 6B is an enlarged schematic view of the left bicycle helmet of FIG. 1 as viewed from the front of the helmet.

FIG. 7 is a bottom plan view of the bicycle helmet of FIG. 1.

FIG. 8 is a partial cross-sectional view of the sides of the bicycle helmet of FIG. 1, as seen from underneath the helmet.

FIG. 8A is an enlarged cross-sectional view of a ventilation opening of the bicycle helmet shown in FIG. 8.

FIG. 9 is a back elevation view of the bicycle helmet of FIG. 1.

FIG. 10 is a left side elevation view of the bicycle helmet of FIG. 1 shown on a user.

FIG. 11 is a left side elevation view of a user on a bicycle wearing the helmet of FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The following detailed description is directed to a specific embodiment of the invention. However, the invention may be embodied in a multitude of different ways as defined and covered by the claims.

Though many styles of bicycle helmets exist, the bicycle helmet of the present application will be discussed with reference to an aerodynamic bicycle helmet such as those used by competitive cyclists. It will be understood that features of the bicycle helmet discussed herein could be used for any helmet design in which low aerodynamic drag is desired and still obtain certain advantages.

FIGS. 1-11 illustrate a preferred embodiment of a protective helmet 10 which is especially well-suited for use as a bicycle helmet. The helmet 10 includes a main unit 36, which is preferably a composite structure, and a retention assembly 80. In the illustrated embodiment, the main unit 36 includes a body 30 and a shell 32. The shell 32 preferably covers at least a portion of an outer surface of the body 30 and, thus, defines at least a portion of the outer surface of the main unit 36. The main unit 36 preferably makes up the protective, impact resistant portion of the helmet 10. Desirably, the main unit 36 includes a ventilation mechanism which provides ventilation for the user and reduces aerodynamic drag. In a preferred embodiment, the ventilation mechanism of the main unit 36 desirably comprises at least one and desirably two ventilation openings or vents 12 located on a side surface of the main unit 36 and an exhaust port 14 located rearward of a plane 66 vertically intersecting the main unit 36 at the location of flow separation from the outer surface of the main unit 36 such that the exhaust port 14 exhausts air into the wake region of the helmet 10. In other embodiments, including the illustrated embodiment, the ventilation mechanism may comprise more or fewer ventilation openings located in other regions of the helmet, such as the front or the top, and still provide certain advantages. The ventilation openings 12 and the exhaust port 14 will be discussed in greater detail below.

To facilitate understanding of the invention, the illustrated embodiment is described in the context of an orientation system based on the orientation of the helmet 10 when worn by a user. As shown in FIGS. 1, 2, and 5, a front surface 34 of the main unit 36 corresponds to an area forward of the location of a plane 56 vertically intersecting the main unit 36 at the maximum width W_(max) (shown on FIG. 7) of the main unit 36 that covers a front portion of the user's head, a rear surface 64 corresponds to an area located rearward of a plane 66 vertically intersecting the main unit 36 at the location of flow separation from the outer surface of the main unit 36 that extends rear of the user's head, and a middle surface 44 corresponds to the area between the plane 56 corresponding to the maximum width W_(max) and the plane 66 corresponding to the location of flow separation. Depending on the geometry of the main unit 36, the plane 66 may be located anywhere between halfway and two-thirds of the distance between the plane 56 and the rear end of the main unit 36. A recessed surface 84 corresponds to an area forward of the ventilation openings 12, as shown in FIGS. 1, 3, 6, and 6A, that at least partially covers the user's forehead and is recessed from the front surface 34 and the middle surface 44. The left side of the main unit 36 corresponds to the user's left side, as shown in FIG. 1 and the right side of the main unit 36 corresponds to the user's right side, as shown in FIG. 2. A leading edge corresponds to an edge closest to the front of the helmet and a trailing edge corresponds to an edge rear of the leading edge.

The front of the main unit 36 desirably has a parabolic shape in a horizontal plane as viewed from above or below, as seen in FIGS. 5 and 7. With reference to FIG. 1A, the main unit 36 of the helmet 10 defines a leading edge A or a forward-most edge of the main unit 36. As used herein, a horizon refers to an imaginary horizontal plane relative to the helmet 10 when the helmet 10 is sitting in a substantially level position parallel to the riding surface on a user. A horizon H passes through the leading edge A as illustrated in FIG. 1A.

As viewed from the front, as illustrated in FIG. 6, the main unit 36 desirably has a substantially round shape, with the shell 32 desirably extending downwards on either side such that the shell 32 covers a user's ears. The front of the main unit 36 desirably extends over a user's forehead such that the main unit 36 fully covers the head of a user without obstructing the user's vision. In one embodiment of the invention, as illustrated in FIGS. 1-3, 6, and 6A, the recessed surface 84 forward of the ventilation openings 12 is shown recessed from the front surface 34 and the middle surface 44. The depth of the recess between the surfaces 84 and 34 at the plane 56 indicating the widest point of the helmet is shown in FIG. 6A as D_(R). D_(R) is desirably the maximum recessed depth with respect to the front and rear parabolas defined by the vertices F and R. In the illustrated embodiment, the depth of the ventilation openings 12 is positive, or towards the inner surface 38 of the main unit 36 as shown. In other embodiments, including the illustrated embodiment, the depth of the ventilation openings 12 may be negative, or outwards of the outer surface of the man unit 36. The recessed surface 84 desirably allows airflow to enter the ventilation openings 12 and manages the boundary layer as will be discussed further below.

The body 30 of the helmet 10 is preferably constructed from an energy absorbing material, such as an expanded foam material, for example. However, other suitable materials may be used. The body 30 may be constructed from a variety of suitable manufacturing techniques that are known or apparent to one of skill in the art. The body 30 may be constructed of a single piece of material or may be constructed of multiple components. If the body 30 is constructed from multiple components, the components may be formed separately and then joined together or may be formed as individual layers of a unitary structure. For example, in one arrangement, multiple components may be joined together by an internal support structure or multiple materials may be molded in successive steps to form a unitary structure. Alternatively, the body 30 could comprise more than one piece secured to the shell 32 and not to one another.

The shell 32 preferably covers a portion of an outer surface of the body 30 and, desirably, provides protection to the body 30 in addition to providing aerodynamic benefits. In addition, the shell 32 may also provide an energy absorbing function. In the illustrated embodiment, the shell 32 covers a substantial portion of the outer surface of the body 30, including front, side, top and rear portions of the body 30. Preferably, the shell 32 is a relatively thin layer of a polycarbonate material. Desirably, an average thickness of the shell 32 is substantially less than an average thickness of the body 30. In one arrangement, the shell 32 may be injection molded onto a body 30 that has been formed in a previous process step. The inside surface of the shell 32 that covers the user's ears may be covered with a liner material such as IEPE; however, other materials may be used. The depth of the body D_(B) is indicated on FIG. 6B as the distance between the interior surface 38 of the body 30 and the interior surface of the shell 32.

Preferably, the helmet 10 also includes a retention assembly 80, which extends below a lower, rearward portion of the main unit 36, as shown in FIGS. 1, 2, 10, and 11. Desirably, the retention assembly 80 is configured to contact a lower, rearward portion of the user's head to assist in securing the helmet 10 onto the user and inhibit undesired movement of the helmet 10.

The inventors recognized that the aerodynamic performance of a bicycle helmet can be affected by the surface roughness of the helmet, which is typically a result of conventional vent placement. In order to reduce the surface roughness factor which contributes to aerodynamic drag, the illustrated embodiment of the present invention desirably eliminates a vent or opening on the front surface 34 of the main unit 36. As shown in FIGS. 1, 2, 5, and 6, the front surface 34 of the main unit 36 desirably has a smooth, continuous surface preferably without any vents or openings. However, in other embodiments, including the illustrated embodiment, the front surface 34 may comprise one or more openings to provide additional ventilation to the rider and still provide certain advantages.

As viewed from the top, shown in FIG. 5, the main unit 36 desirably comprises two smooth parabolic surfaces at the front and the rear but tapers to a blunt end at the rear. Point F is the vertex of the parabolic front surface and point R is the vertex of the parabolic rear surface. The top of the main unit 36 is a substantially smooth and continuous surface and preferably lacks ventilation openings. The elimination of ventilation openings on the top of the main unit 36 desirably reduces the surface roughness of the helmet 10 in order to minimize the aerodynamic drag which would be caused by these openings. However, in other embodiments, including the illustrated embodiment, the top of the main unit 36 may comprise one or more openings to provide additional ventilation to the rider and still provide certain advantages. The plane 56 intersecting the main unit 36 at the maximum width of the main unit 36 is depicted in FIGS. 1, 2, 5, and 7. As will be discussed in further detail below, the ventilation openings 12 are preferably located to the rear of the plane 56 of the main unit 36.

The rear portion of the main unit 36 is also substantially parabolic as viewed from the front or the back but, in the illustrated embodiment shown in FIGS. 1-11, preferably may have a blunt end rather than a smooth parabolic arc or point. The edges of a rear-facing surface such as blunt surface 35 are preferably defined by the substantially curved arc of the rear surface 64 of the main unit 36 and an underside surface 37, as shown in FIGS. 3, 4, 7, and 9. In some embodiments, including the illustrated embodiment, the top arc of the main unit 36 may extend farther towards the rear of the main unit 36 than the underside of the main unit 36, as shown most clearly in the left and right side views illustrated in FIGS. 1 and 2. A trailing top edge 76 and a trailing bottom edge 78 are shown in FIGS. 1 and 2. The rear surface 64 of main unit 36, blunt surface 35, and underside surface 37 preferably define a hollow space at the rear of the helmet 10. Preferably, the blunt surface 35 defines an exhaust port 14 located between the trailing top edge 76 and the trailing bottom edge 78. The exhaust port 14 may be centered within the blunt surface 35 or may be located anywhere within the blunt surface 35. In the illustrated embodiment, one exhaust port 14 is shown. However, multiple exhaust ports may be included. Furthermore, the exhaust port 14 is shown on the blunt surface 35 but may be located anywhere within the rear surface 64 or the underside surface 37 and still provide a helmet having some advantages. Further details relating to the exhaust port 14 as part of the ventilation mechanism of the helmet 10 will be discussed below.

The underside of the main unit 36 preferably defines an inner surface 38, as seen in FIGS. 3, 4, and 7. The inner surface 38 desirably comprises the inner surface of body 30 and may be contoured or flat, depending on the desired interior airflow characteristics or user comfort preferences. As shown in FIG. 7, the concave opening of main unit 36 is preferably shaped to fit a user's head without having open space rear of the user's head. As discussed above, a rear portion of the underside of the main unit 36 extends beyond the back of the user's head and defines the underside surface 37. The inside of the main unit 36 within the space defined by the inner surface 38, the blunt surface 35 (seen most clearly in FIG. 9), and the underside surface 37 is preferably substantially hollow such that air may flow through the area and exit the main unit 36 via the exhaust port 14, as will be discussed in greater detail below.

As discussed above, FIGS. 1 and 2 depict left and right side views of the helmet 10. These figures most clearly illustrate the preferable location of ventilation openings 12. In the illustrated embodiment in FIGS. 1-11, one ventilation opening is located on each side of the main unit 36 within the middle surface 44. A greater or lesser number of ventilation openings 12 may be placed on the sides of the main unit 36, depending on the desired ventilation and airflow characteristics. FIGS. 1-3, 6, and 6A illustrate that the surface of the main unit 36 may desirably include portions that recess inward from the smooth parabolic surface leading to the ventilation openings 12. As shown in FIGS. 1-3, 6, and 6A, the surface of the main unit 36 is smooth and parabolic without respect to the recessed portions. In other embodiments, including the illustrated embodiment, the surface of the main unit 36 may not include any recessed portions. A leading edge 112 of the ventilation opening 12 and a trailing edge 212 of each of the ventilation openings 12 are shown in FIG. 8. As shown in FIGS. 1-3, 6A, 8, and 8A, the leading edge 112 of the ventilation openings 12 may be equal to the surface of the main unit 36 or the leading edge 112 of the ventilation openings 12 may be recessed inward a depth D_(R) from the middle surface 34 of the main unit 36.

The placement of the ventilation openings will affect the surface roughness of the helmet 10 which will in turn affect the aerodynamic drag, as discussed above. The placement of the ventilation opening 12 is an important issue when designing the bicycle helmet 10 for maximum drag reduction, as conventional vent placement can cause significant aerodynamic drag. In a preferred embodiment designed to minimize aerodynamic drag, such as that shown in FIGS. 1-11, the surface 84 in front of the ventilation openings 12 is recessed from the front surface 34 of the main unit 36. In other embodiments, including the illustrated embodiment, the trailing edge 212 of the ventilation openings 12 may be above the outer surface of the main unit 36 and still provide certain advantages.

The geometry of the ventilation openings 12, including the cross sectional area, the ventilation opening 12 orientation, the height H of the ventilation opening 12, the width W of the ventilation opening 12, and the depth D_(R) of the ventilation opening 12 influence the effectiveness of the ventilation mechanism and the aerodynamics of the helmet 10. Desirably, the depth D_(R) is minimized in order to keep the frontal area of the main unit 36 as small as possible. Ventilation openings 12 on a main unit 36 are generally designed to promote the transfer of heat from the head of a user through forced convection. In the helmet 10 illustrated in FIGS. 1-11, the ventilation openings 12 and the exhaust port 14 are designed to achieve optimal heat removal by allowing air to enter the main unit 36 through the ventilation openings 12, flow over the user's head, and exit the main unit 36 through the exhaust port 14 at the rear of the main unit 36 into the wake region of the helmet 10.

In some embodiments, including the illustrated embodiment, the ventilation openings 12 are preferably oriented such that the cross section of the openings 12 is perpendicular to a local flow direction 22 at the opening 12. The line 22, shown in FIGS. 3, 4, and 7 indicates a flow of air along the outer surface of the main unit 36. The ventilation openings 12 are placed such that the direction of the local airflow 22 is perpendicular to the height H of the ventilation opening, as shown in the illustrated embodiment. The airflow 22 enters the main unit 36 through the ventilation openings 12, flows through the interior of the main unit 36 and exits the main unit 36 through exhaust port 14, as shown in FIGS. 3, 4, and 7. This flow of air desirably provides ventilation to the user by conducting heat away from the head of the user. The height H of the openings 12 is preferably substantially larger than the width W of the openings. In some embodiments, including the illustrated embodiment, the height H of the ventilation opening 12 is desirably between 2-10 times the width W, more desirably between 4-8 times the width W, and most desirably between 6-8 times the width W. The height H of the ventilation openings 12 may be greater than 10 times the width W. In some embodiments, including the illustrated embodiment, the height H of the ventilation openings 12 is at least 4 times the width W, at least 5 times the width W, at least 6 times the width W, at least 7 times the width W, or at least 8 times the width W. In some embodiments, including the illustrated embodiment, the width W and the depth of the ventilation openings 12 may vary from top to bottom along the height H of the ventilation openings 12. The depth of the ventilation openings 12 may be dependent on the geometry of the main unit 36. The height H of the ventilation openings 12 is desirably between 2-25 times the depth, more desirably between 5-15 times the depth, and most desirably between 10-15 times the depth. The height H of the ventilation openings 12 may be greater than 25 times the depth. In some embodiments, including the illustrated embodiment, the height H of the ventilation openings 12 is at least 4 times the depth, at least 8 times the depth, at least 10 times the depth, at least 15 times the depth, or at least 25 times the depth.

The ventilation openings 12 are used to manage the boundary layer by removing or diverting low energy boundary layer flow from the outside of the main unit 36 to the inside of the main unit 36 to allow the airflow to remain attached to the outside surface of the main unit 36 further down the main unit 36. The detachment of the boundary layer from the surface of the main unit 36 rearward of the plane 56 creates a high pressure zone or area of flow stagnation between the neck and shoulders of the user. This high pressure zone increases aerodynamic drag. The ventilation openings 12 are desirably placed such that the openings 12 are located in the region rear of the plane 56 indicating the widest point of the main unit 36 and in front of the plane 66 indicating the area of flow separation from the helmet, which may be located anywhere between halfway and two-thirds of the distance between the plane 56 and the rear of the main unit 36 as measured from the plane 56, as discussed above and shown in FIGS. 1, 2, 7, and 8. Advantages may be achieved by locating the ventilation openings 12 forward of a plane located halfway between the plane 56 and the rear of the main unit 36. Advantages may also be achieved by locating the ventilation openings 12 forward of a plane located two-thirds of the distance from the plane 56 to the rear of the main unit 36 as measured from the plane 56. Placing the ventilation openings 12 in this region will preferably allow the boundary layer to remain attached further down the main unit 36, thus reducing the aerodynamic drag of the helmet 10 by reducing the high pressure zone that results from airflow detachment. Additionally, the placement of the ventilation openings 12 in front of the plane 66 indicating the area of flow separation from the main unit 36 will help to prevent flow stagnation around a user's shoulders and neck, further improving the aerodynamic performance of the helmet 10. In other embodiments, including the illustrated embodiment, depending on the geometry of the main unit 36, the ventilation openings 12 may be located forward of the widest cross section of the main unit 36 but most desirably the ventilation openings 12 are located forward of the location of flow separation from the outer surface of the main unit 36.

Although this invention has been disclosed in the context of certain preferred embodiments and examples, it will be understood by those skilled in the art that the present invention extends beyond the specifically disclosed embodiments to other alternative embodiments and/or uses of the invention and obvious modifications and equivalents thereof. In addition, while a number of variations of the invention have been shown and described in detail, other modifications, which are within the scope of this invention, will be readily apparent to those of skill in the art based upon this disclosure. It is also contemplated that various combinations or sub-combinations of the specific features and aspects of the embodiments may be made and still fall within the scope of the invention. Accordingly, it should be understood that various features and aspects of the disclosed embodiments can be combined with or substituted for one another in order to form varying modes of the disclosed invention. Thus, it is intended that the scope of the present invention herein disclosed should not be limited by the particular disclosed embodiments described above, but should be determined only by a fair reading of the claims that follow. 

What is claimed is:
 1. A bicycle helmet comprising: a main unit having a cavity configured to receive a user's head, said main unit comprising a shell and a body, said main unit defining a front surface and a rear surface which have a parabolic profile when viewed from above when the user is in an aerodynamic position with the user's head lowered; a ventilation mechanism comprising at least one ventilation opening formed in a side surface of said main unit rearward of a widest vertical cross section of the main unit, said ventilation opening having a height, a width, and a depth, and an exhaust port in a rear portion of the main unit wherein the height of the ventilation opening transverse to a local flow direction at said ventilation opening is the largest dimension of the ventilation opening; wherein said ventilation mechanism provides an airflow through said main unit due to airflow entering the main unit through the at least one ventilation opening and exiting the main unit through the exhaust port.
 2. The bicycle helmet of claim 1, wherein the local flow direction at the ventilation opening is perpendicular to the height of the ventilation opening.
 3. The bicycle helmet of claim 1, wherein said exhaust port comprises at least one opening in the rear of the main unit.
 4. The bicycle helmet of claim 1, where said exhaust port is located below a trailing top edge of the helmet.
 5. The bicycle helmet of claim 1, wherein said exhaust port is located below a trailing bottom edge of the helmet.
 6. The bicycle helmet of claim 1, wherein said ventilation opening is located forward of a plane defined by flow separation from the surface of the helmet.
 7. The bicycle helmet of claim 1, wherein the height of said ventilation opening is substantially more than the width of said ventilation opening.
 8. The bicycle helmet of claim 7, wherein the height of said ventilation opening is 6 times the width.
 9. The bicycle helmet of claim 7, wherein the height of said ventilation opening is 8 times the width.
 10. The bicycle helmet of claim 7, wherein the height of said ventilation opening is 6-8 times the width.
 11. The bicycle helmet of claim 1, wherein a leading edge of said ventilation opening is formed in line with the side surface of the helmet.
 12. The bicycle helmet of claim 1, wherein a leading edge of said ventilation opening is recessed inward from the side surface of the helmet.
 13. The bicycle helmet of claim 1, wherein said rear surface tapers toward the rear of said body.
 14. The bicycle helmet of claim 1, wherein said helmet has a substantially teardrop shape.
 15. The bicycle helmet of claim 13, wherein said rear surface is bobbed to reduce the length of said body.
 16. The bicycle helmet of claim 1 further comprising a top surface, wherein said top surface does not comprise any openings.
 17. The bicycle helmet of claim 1 further comprising a front surface, wherein said front surface does not comprise any openings.
 18. The bicycle helmet of claim 1 further comprising a substantially hollow rear portion of the helmet extending from the back of a user's head to the exhaust port, said rear portion formed such that a bottom surface of the rear portion is substantially flat and an upper surface of the rear portion is curved.
 19. The bicycle helmet of claim 1, wherein said ventilation opening is located forward of a plane located half of the distance rearward from the widest cross section of the helmet to the rear of the helmet.
 20. The bicycle helmet of claim 1, wherein said ventilation opening is located forward of a plane located two-thirds of the distance rearward from the widest cross section of the helmet to the rear of the helmet as measured from the widest cross section of the helmet.
 21. A bicycle helmet comprising: a body having a cavity configured to receive a user's head; a ventilation mechanism comprising at least one ventilation opening formed in a side surface of said main unit rearward of the widest cross section of the main unit and an exhaust port formed substantially in a rear portion of the main unit; wherein said ventilation mechanism provides a flow of air through said main unit due to airflow entering the main unit through the at least one ventilation opening and exiting the main unit through the exhaust port.
 22. A method for reducing aerodynamic drag while operating a bicycle, the method comprising: providing an aerodynamic bicycle helmet comprising a body having a cavity configured to receive a user's head, a ventilation mechanism comprising at least one ventilation opening formed in a side surface of said helmet rearward of the widest cross section of the main unit and an exhaust port formed in a rear portion of the main unit; placing said helmet on the user's head; orienting the user's head while operating a bicycle such that a local airflow direction at the ventilation opening is perpendicular to said opening; and allowing said airflow to enter the helmet through said ventilation opening and exit the helmet through said exhaust port. 